Why don't I stutter when someone says ''Repeat after me..." even if it's a difficult word?

Why don't I stutter when someone says ''Repeat after me..." even if it's a difficult word? For example, I want to say a sentence that has a difficult word for me. When I say it on my own, I stutter. When someone else tells me to repeat a sentence, I don't stutter. I don't get it, why?